    Patent Literature 1: JPH9-274935A    Patent Literature 2: JP2000-251923A
Recently, lithium ion secondary batteries attract attentions as an example of secondary batteries which can be applied to an electric vehicle, a hybrid vehicle, a UPS (uninterrupted power supply), or the like, and easily accomplishing miniaturization and a large capacity. A lithium ion secondary battery generally comprises an internal electrode pair (stacked body) in sheet type having a sheet positive electrode, comprised of a sheet cathode collector and a cathode active material coated thereon, a sheet negative electrode, comprised of a sheet anode collector and an anode active material coated thereon, and a separator, wherein the sheet positive electrode and the sheet negative electrode are stacked with each other via the separator. The lithium ion secondary battery also comprises a battery casing airtightly sealing and covering the internal electrode pair, and containing an electrolysis solution inside the battery casing, and a positive electrode terminal and a negative electrode terminal respectively connected to the positive electrode of the internal electrode pair and the negative electrode thereof inside the battery casing. In the case of charging, lithium ions from the cathode active material move via the electrolysis solution and the separator, and are intercalated to the anode active material, while in the case of discharging, the lithium ions move in the reverse order. In this fashion, the secondary battery performs charging/discharging.
As an example of the foregoing internal electrode pair comprising the separator and the sheet electrodes, there is known a stacked body having a separator present between sheet electrodes and formed successively in order to suppress any battery breakdown due to an internal short-circuit and any influence thereof to surrounding parts (see, for example, patent literatures 1 and 2).
Patent literature 1 discloses a lithium ion secondary battery which has an internal electrode pair (stacked body) that comprises electrode units successively stacked one another. Each electrode unit has a separator farmed of two microporous films pasted together in an envelope-like form, and a sheet electrode accommodated in the interior of the envelope-like separator in order to suppress any propagation effect of an internal short-circuit and to improve the heat dissipation performance.
Moreover, patent literature 2 discloses a rectangular secondary battery having an internal electrode pair (stacked body) that comprises a long and strip-shaped separator which has a folded bottom end and which is folded in a zigzag manner, and positive/negative sheet electrodes alternately arranged between respective folded portions of the successive separator in order to eliminate a dead space and to increase the battery capacity.